Differentially flatness active disturbance rejection control approach via algebraic parameter identification to double tank problem

The flatness-based active disturbance rejection control (ADRC) approach via online algebraic parameter identification is proposed to deal with the double tank problem. The control task is to maintain the lower tank level at a desired value by manipulating the inlet regulating valve. Firstly, the double tank problem is formulated based on the designed double tank platform, where the process input and output data are available in real-time in Matlab software installed in the upper monitor and the ABB AC800M in the lower computer. Then, the algebraic parameter identification algorithm is proposed to identify the unknown parameters of a typical second-order process, which was a flatness system with the lower tank level as the flat output. All the unmodelled dynamics, as well as the external disturbances are regarded as the total disturbance. Based on the identified model parameters of the process, an extended state observer is constructed to estimate the the flat output and its time derivative, as well as the total disturbance in real-time. A linear feedback control law is then designed to steer the lower tank level following the desired trajectory of the flat output, and thus the flatness-based ADRC approach is designed. The effectiveness of the proposed approach is validated by the simulation results based on the practical process input and output data in the platform.